A wide variety of food products, such as pasta, beans, corn, peas, and other vegetables and fruit, are processed every day around the world by blanching or heating. For many years, the basic rotary blancher consisted of an elongate cylindrical perforate drum received in a tank filled with heated water. Food products are continuously introduced through an inlet in one end of the drum and heated by the water in the tank. During operation, flights of a helical auger in the drum rotate and urge the food products from the drum inlet toward a drum outlet.
However, food products tend to clump together as the drum rotates resulting in poor heat transfer and uneven heating, especially for those food products in the middle of the clump. To combat this problem, straight and curved baffles have been employed between adjacent flights of the auger to lift and tumble food product during rotation of the drum to help improve heat transfer and more evenly heat food product. Examples of such baffles are disclosed in Zittel, U.S. Pat. Nos. 5,632,195 and 5,456,091. As a result of this improvement, blanching capacity was not only roughly doubled, but the food products were more uniformly blanched. For example, where nine inches of one specific type of food product could previously be blanched, a blancher equipped with these baffles could more uniformly blanch about eighteen inches of the same food product.
In addition to this type of mechanical agitation, other methods have also been employed to improve heat transfer. For example, as is disclosed in Zittel, U.S. Pat. Nos. 5,752,431 and 5,632,195, air and steam have been introduced into the water in the tank to help increase heat transfer efficiency. Air has also been used to improve cooling efficiency in food cooling applications. For example, U.S. Pat. No. 4,875,344 discloses injecting relatively low volumes of low-pressure air, namely warm air into cold water, to improve cooling of food products in a rotary drum chiller. In some food product cooling applications, manifolds connected to nozzles that introduce the air into the chiller have been located between the tank and drum at the five o'clock and seven o'clock positions relative to the drum's center. However, in each of these applications, the air was injected at a pressure of no greater than 150 pounds per square inch (psi) at a flow rate no more than 25 cubic feet per minute (CFM).
Directed flows of water have also been used to increase heat transfer. For example, U.S. Pat. No. 5,456,091 discloses improved cooling by directing flows of water from nozzles connected to a manifold toward the drum to agitate food products in the drum. However, a relatively low volume of water of no more than 8 gallons per minute per foot of blancher length (gpm/ft) at a pressure no greater than 40 psi was used for these cooling applications. While directed flows of water have also been tried in blanchers to improve heat transfer, it has been done using pressures no greater than 8 psi and flow rates no greater than 10 gpm/ft.
It is believed that greater pressures and flow rates of directed water flows have not been tried before because the lower pressures and flow rates previously tried did not increase efficiency so dramatically as to predict a correspondingly greater efficiency increase. Moreover, the cost of bigger and more powerful pumps and other equipment needed to deliver greater flow rates, particularly at higher pressures, was thought to be so cost prohibitive that any possible performance advantage was believed not to be worth it.
It has always been very difficult for rotary blanchers to process food products that are relatively heavy, typically having a density greater than 55 pounds per cubic foot (lbs/ft.sup.3). Examples of food products that are relatively heavy include packaged meats, such as hot dogs and turkey breasts, as well as other types of food products that are not packaged. While baffles have been used to help turn over and agitate food products during operation, heavier food products tend to clump together on the bottom and along the side of the rotating drum where the drum leaves the water. This is believed to be caused, at least in part, by the increased weight of the food products causing them to sink and by the increased friction between the food products and the rotating drum.
Testing has shown that, most, if not virtually all, heavy food products congregate along one side of the drum near the bottom of the drum in a region that occupies less than about 20% of the total volume of the drum dramatically reducing the amount of food product surface area actually exposed directly to the hot water. By congregating in a clump, the food products inside the clump are not heated directly by the water but by other outer food products, which means it takes more time to heat all of the food products to the desired temperature than is acceptable. Other experiments have shown that these lower turbulence (i.e. lower volume and pressure) flows of air and water used in the past, even if the blancher is equipped with agitating baffles, will not break up and agitate heavy food products enough to achieve the desired level of heat transfer needed to make blanching of heavy food products commercially viable.
Pasta is a relatively heavy food product that has a density less than 55 lbs/ft.sup.3. Pasta, however, is relatively fragile and must be handled much more carefully during blanching than most other types of food products, which has limited attempts in the past to increase heat transfer. Past attempts to increase heat transfer include the use of baffles and the introduction of air having a pressure no greater than 2 psi at a volume no greater than 40 CFM per foot of blancher length. As a result, throughput for a 72-inch diameter blancher has been heretofore limited to about 3500 pounds of pasta per hour, making production undesirably slow.
While the food processing industry has always been driven to find ways of processing more food product faster, it has been more recently been tempered by the need to do so in a manner that ensures the food is not contaminated. Thus, there has been a move to not only heat the food products until they are cooked, but to pasteurize the food products which takes longer, requires more heat, and thus is more costly.
Consequently, there has arisen a great need for a method and rotary blancher that processes food products, including heavy and fragile food products, more efficiently and more quickly and which is capable of more cost-effectively cooking, blanching and pasteurizing food products.